Rectangular trimmer potentiometer



Nov. 19, 1968 J WOQDS ET AL RECTANGULAR TRIMMER POTENTIOMETER 2 Sheets-Sheet 1 Filed Aug. 8, 1967 6 6 a m 3 a x M 0 0 HI, 8 6 0 2 m 6 I 44 5 4 L I 0 n E 0 u /8 Q- 2 7 I 8 l 6 -r m 12 J a 5 l INVENTORS JOHN G. WOODS GEORGE W WOOD M jl ATTORNEY Nov. 19, 1968 J.G. wooos ET ALv 3,412,362

RECTANGULAR TRIMMER POTENTIOMETER Filed Aug 8, 1967 2 Sheets-Sheet 2 is m; F/G4 V4 5" 78 l8 I. 74 \II 2 IN VE N TORS.

JOHN G. WOODS GEORGE W WOOD ATTORNEY United States Patent 3,412,362 RECTANGULAR TRIMMER POTENTIOMETER John G. Woods, Philadelphia, Pa., and George W. Wood,

Hammonton, N.J., assiguors to IRC, Inc., Philadelphia, Pa.

Filed Aug. 8, 1967, Ser. No. 659,055 7 Claims. (Cl. 338-183) ABSTRACT OF THE DISCLOSURE A potentiometer comprising a rectangular housing having an enclosed, rectangular cavity therein. A resistance element extends longitudinally along the bottom of the cavity, and a collector member extends longitudinally along the bottom of the cavity in spaced, parallel relation to the resistance element. Terminals are secured to the ends of the resistance element and extend through the bottom of the housing, and a terminal is secured to the collector and extends through the bottom of the housing. A threaded shaft is rotatably supported in the housing and extends longitudinally through the cavity above and parallel to the resistance element and collector member. The shaft extends beyond one end of the housing to permit rotation of the shaft. A contact carrier is mounted on the shaft within the cavity for longitudinal movement along the shaft upon rotation of the shaft. A contact member is mounted on the contact carrier for movement therewith. The contact member has one arm slidably engaging the resistance element and a second arm slidably engaging the collector member.

Background With the trend toward miniaturization of electronic devices, there has been developed several types of miniature variable resistors or potentiometers. One such type of miniature potentiometer is the rectilinear potentiometer. This type of potentiometer includes an elongated resistance element and an elongated collector member arranged in parallel, spaced relation in a rectangular housing. A threaded shaft is rotatably supported on the housing and extends parallel to the resistance element and collector member. A contact is mounted on the shaft so that rotation of the shaft moves the contact longitudinally along the shaft. The contact slidably engages the resistance element and the collector member. In designing this type of potentiometer, it is desirable that the parts of the potentiometer be of simple design and capable of being easily assembled together in the smallest possible housing. This is of particular importance in a miniaturized potentiometer wherein the parts are extremely small in size and therefor diflicult to handle. In addition, the design of the parts must provide a rugged construction which will operate properly both mechanically and electrically.

Summary It is an object of the present invention to provide a novel rectilinear potentiometer.

It is another object of the present invention to provide a rectilinear potentiometer which can be easily assembled so that it is inexpensive to manufacture.

It is a further object of the present invention to provide a rectilinear potentiometer assembled in a small housing.

It is a still further object of the present invention to provide a miniature rectilinear potentiometer including a slip clutch arrangement between the contact carrier and the shaft.

It is still another object of the present invention to provide a miniature rectilinear potentiometer having a seal ice around each terminal where the terminal projects from the housing.

Other objects will appear hereinafter.

Brief description of drawings For the purpose of illustrating the invention, there is shown in the drawings a form which is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown.

FIGURE 1 is a perspective view of the potentiometer of the present invention.

FIGURE 2 is a top plan view of the potentiometer of the present invention with the cover removed.

FIGURE 3 is a longitudinal, sectional view taken along line 33 of FIGURE 2.

FIGURE 4 is a longitudinal sectional view taken along line 4-4 of FIGURE 2.

FIGURE 5 is a transverse, sectional view taken along line 55 of FIGURE 4.

FIGURE 6 is a perspective view of the contact used in the potentiometer of the present invention.

Description of invention Referring to the drawing, the potentiometer of the present invention is generally designated as 10. In general, the potentiometer 10 comprises a rectangular housing 12 having an enclosed cavity therein. A resistance element 14 is mounted in the housing and extends longitudinally along the bottom of the cavity. A collector member 16 is mounted in the housing and extends longitudinally along the bottom of the cavity parallel to, but spaced slightly from, the resistance element 14. A threaded shaft 18 is rotatably mounted on the housing 12 and extends longitudinally across the cavity parallel to and spaced above the resistance element 14 and the collector member 16. The shaft 18 projects beyond one end of the housing 12 so that it is accessible for rotation from outside the housing. A contact 20 is carried on the shaft and slidably engages the resistance element 14 and the collector member 16. Rotation of the shaft 18 moves the contact 20 longitudinally in the housing 12 to vary the resistance value setting of the potentiometer 10.

The housing 12 comprises a rectangular bottom section 22 and a rectangular cover plate 24 both of an electrical insulating material, such as a plastic. The bottom section 22 has a rectangular cavity 26 in its top surface to provide the bottom section with a pair of parallel side walls 28 and 30, a front end wall 32, a rear end wall 34, and a bottom wall 36. The front end wall 32 and rear end wall 34 have aligned, longitudinally extending bearing grooves 38 and 40 respectively in their top surfaces. The bearing groove 38 extends completely across the front end wall 32 whereas the bearing groove 40 extends only partly across the rear end wall from its inner surface. A retainer groove 42 is provided in the top surface of the front end wall 32 and extends transversely across the bearing grooves 38. As shown in FIGURE 5, a divider rib 44 projects upwardly from the bottom wall 36 and extends longitudinally along the bottom wall. The divider rib 44 is positioned closer to the side wall 28 than to the side wall 30 so as to provide a narrow space between the driver rib and the side wall 28 and a wide space between the divider rib and the side wall 30. The bottom wall 36 has two openings 37 therethrough at the side wall 30 and adjacent the end walls 32 and 34. Conical bosses 39 project from the outer surface of the bottom wall 36 at each of the openings 37 with the openings extending through the bosses. A third opening 41 extends through the bottom wall 36 at the side wall 28. A conical boss 43 extends from the outer surface of the bottom wall 36 at the third 3 opening 41 with the opening extending through the boss 43.

The cover 24 extends over and is secured to the top surface of the bottom section 22 so as to enclose the cavity 26. The cover 24 may be secured to the bottom section by a suitable cement. The cover 24 has a shallow, rectangular cavity 46 in its inner surface which mates with the cavity 26 in the bottom section 22. Bearing grooves 45 and 47 are provided in the bottom surface of the 'cover 24 at the ends thereof. The bearing grooves 45 and 47 mate with the bearing grooves 38 and 40 respectively in the bottom section 22. A retainer groove 49 is provided in the bottom surface of the cover 24. The retainer groove 49 extends transversely across the bearinggroove 45 and mates with the retainer groove 42in the bottom section Resistance element 14 comprises a rod 48 of an electrical insulation or electrically insulating material, such as a plastic, ceramic or a wire coated with insulation, and" aresistance material 50 on the surface of the rod 48. As' shown, the resistance material is a wire of a resistance material helically wound around the rod. However, the resistance materials can be a film of any of the well-known resistance materials coated on the surface of the rod. The resistance element 14 is seated on and extends along the bottom wall 36 in the wide space between the divider rib 44 and the side wall 30. A pair of metal terminal strips 52 are secured to the resistance material 50 adjacent the ends of the rod 48 such as by welding, soldering or by a suitable cement. The terminal strips 52 extend down- Wardly through the openings 37 in the bottom wall 36 and project beyond the bottom wall.

Each of the terminal strips 52 has a pair of notches 53 in its side edges at a point within the bosses 39. The material of the bosses 39 extends into the notches so as to prevent upward movement of the terminal strips and thereby secure the resistance element 14 in place on the bottom wall. The material of the bosses 39 is forced into the notches 53 by heating the bosses and compressing them around the terminal strips 52. This also compresses the bosses 39 around the terminal strips 52 so as to form a seal therebetween which prevents dirt and moisture from entering the cavity 26.

Collector member 16 comprises a thin, rectangular strip 54 of an electrically conductive metal which is seated in the narrow space between the divider rib 44 and the side wall 28 and extends along substantially the entire length of the bottom wall 36. At the top of the rib 44, the collector strip 54 is bent along its entire length so as to extend away from the side wall 28. Thus, the top edge of the collector strip 54 is spaced between the side wall 28 and the resistance element 14 so that it can be easily engaged by the contact 20. The height of the collector strip 54 is substantially equal to the diameter of the resistance element 14. A terminal strip 56 extends from the bottom edge of the col-lector strip through the opening 41 in the bottom wall 36 and projects beyond the bottom wall. Terminal strip 56 has a pair of notches 57 in its side edges and the material of the boss 43 extends into the notches to secure the collector 16 in position on the bottom wall. The boss 43 also fits tightly around the terminal strip 56 to form a seal therewith.

Shaft 18 has a bearing portion 58 at one end which is rotatably supported in the mating bearing grooves 40 and 47, and a bearing portion 60 adjacent its other end which extends through and is rotatably supported in the mating bearing grooves 38 and 45. Thus, the shaft 18 extends longitudinally across the cavity 26 in the housing 12 parallel to and above the resistance element 14 and collector member 16. Between the bearing portions 58 and 60, the shaft 18 has a threaded portion 62. At the front bearing portion 60, the shaft 18 has an annular flange 64 which fits into the mating retainer grooves 42 and 49. This prevents longitudinal movement of the shaft 18 with respect to the housing 12, but allows the shaft to rotate 4 r. with respect to the housing. The front end of the shaft 18 projects beyond the front end wall 32 of the housing 12 and has an enlarged head 66 thereon by which the shaft can be rotated.

A substantially U-shaped contact carrier 68 of an electrical insulating material, such as a plastic, is mounted within the cavity 26 on the threaded portion 62 of the shaft 18. Contact carrier 68 has a base 70 with a fiat bottom surface and apair of spaced arcuate arms 72 .extending upwardly from the base. The outer surface-74 of each-ofthe arms 72 is concave and the inner, surface 76 of each of the arms is convex; The inner surfaces 76 of the arms 72 are provided with opposed grooves 78 which are diametrically opposite segments of a cylinder. A boss 80 projects downwardly from the bottom surface of the base 70. The contact carrier 68 is mountedon the threaded portion 62 of the shaft 18 with-its base-70 extending between the shaft and the resistance element 14 and collector member16, and its arms 72 extending along ,oppo-' site sides of the shaft. The shaft 18 fits in-the grooves 78 in the contact carrier arms 72., The surfaceof the grooves 78 is either prethreaded to correspond with the threads of the shafts or the threads of the shaft indent the surface of the grooves to form mating threads therein. The spacing between the inner surfaces 76 of the arms 72 is such that the arms grip the shaft so as to hold the contact carrier 68 on the shaft. The width of the contact carrier 68 is substantially equal to the distance between the side walls 28 and 30 of the housing 12. Therefore, the ends of the contact carrier arms 72 engage the sides of the cover cavity 46 and the sides of the base 70 engage the side walls 28 and 30 so as to prevent rotation of the contact carrier with respect to the housing 12.'Thus, rotation of the shaft 18 moves the contact carrier 68 longitudinally along the shaft. Thecontact carrier 68 is of a length that it will engage the end walls 32 and 34 .ofthe housing 12 before leaving the threaded portion 62 of the shaft 18. When the contact carrier 68 does engage one of the end walls of the housing 12, continued rotation of the shaft will cause the arms 72 to spread apart, ,which they can do because of their shape, and allow the threads of the shaft to slip. Thus, there is provided a slip clutch arrangement which allows the continuation of rotation of the shaft Without damaging the contact carrier 68.

The contact 20 comprises a rectangular metal plate 82 of the same size and shape as the bottom surface of the base 70 of the contact carrier 68, and a pair of parallel arms 84 and 86 extending from one end ofthe plate 82 back under the plate. Contact lips 88 and 90 are provided on the ends of the arms 84 and 86 respectively. Contact lip 90 has a curved depression 91 in its bottom surface. The plate 82 has a hole 92 therethrough which has one sharp edge. The contact 20* is mounted on the contact carrier 68 with the plate 82 seated against the bottom surface of the base 70 and the contact arms extendingv downwardly toward the resistance element 14 and collector 16. The contact arms 84 and 86 are of a length that the lips 88 and 90 slidably engage the resistance material 50 of the resistance element 14 and the upper edge of the collector 16 respectively. The upper edge of the collector 16 fits in the depression 91 in the contact lip 90 so that the contact lip will remain on the collector. The boss 80 projecting from the bottom surface of the contact carrier 68 extends through the hole 92 in the contact plate 82 and the sharp edge of the hole 92 bites into the boss 80 to secure the contact 20 to the contact made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A potentiometer comprising:

a rectangular housing of an electrical insulating material, said housing having an enclosed rectangular cavity therein formed by a pair of parallel side walls,

a pair of end walls extending between said side walls, a

bottom wall and a top wall; resistance element within said cavity and extending along the bottom wall; collector member within said cavity and extending along the bottom wall in parallel spaced relation to said resistance element; threaded shaft extending longitudinally through the cavity over and substantially parallel to the resistance element and the collector member, said shaft being rotatably supported in the end walls of the housing and projecting beyond one end Wall so as to be accessible for rotation of the shaft;

a contact carrier of a resilient plastic material mounted on the threaded shaft, said contact carrier having a base which extends between the shaft and the bottom wall of the housing and a pair of spaced arms extending from the base toward the top wall of the housing and gripping the shaft therebetween, the free ends of said contact carrier arms engaging the side walls of the housing, but being spaced from the top wall of the housing, so as to prevent rotation of the contact carrier with the shaft but permit the contact carrier to move longitudinally along the shaft as the shaft rotates, at least a portion of said arms spaced from the free ends of the arms being spaced from the side walls of the housing so that the arms can expand away from the shaft when the contact carrier engages the end walls of the housing and provides a slip clutch between the contact carrier and the shaft; and

a metal contact carried by the contact carrier, said contact having one arm slidably engaging the resistance element and a second arm slidably engaging the collector member.

2. A potentiometer in accordance with claim 1 in which the outer surfaces of the contact carrier arms are concave and the inner surfaces of said arms are convex.

3. A potentiometer in accordance with claim 2 in which the inner surfaces of the contact carrier arms are provided with opposed grooves which are diametrically opposed segments of a cylinder, and the shaft fits in said grooves.

4. A potentiometer in accordance with claim 2 in which the width of the contact carrier at the base and at the ends of the arms is substantially equal to the distance between the side walls of the housing so that the base and the ends of the arms engage the side walls to prevent rotation of the contact carrier with the shaft.

5. A potentiometer in accordance with claim 1 in which the collector member is a rectangular metal strip having one edge seated on and extending along the bottom wall of the housing, and the second arm of the contact has a lip on its end which slidably engages the opposite edge of the collector member and the lip has a curved depression in its bottom surface in which the edge of the collector member fits.

6. A potentiometer comprising:

a rectangular housing of an electrical insulating material, said housing having an enclosed rectangular cavity therein formed by a pair of parallel side walls, a pair of end walls extending between said side walls, a bottom wall and a top wall;

a resistance element within said cavity and extending along the bottom wall;

a pair of metal terminal strips secured to the resistance element adjacent the ends of the resistance element, said terminal strips extending through and projecting beyond the bottom wall of the housing, a separate boss projecting from the bottom wall of the housing around each of said terminal strips, each of said terminal strips having at least one notch in an edge thereof within the boss, and the bosses extending into the notches to prevent movement of the terminal strips with respect to the housing;

a collector member within said cavity and extending along the bottom wall in parallel spaced relation to said resistance element;

a threaded shaft extending longitudinally through the cavity over and substantially parallel to the resistor element and the collector member, said shaft being rotatably supported in the end walls of the housing and projecting beyond one end wall so as to be accessible for rotation of the shaft;

a contact carrier of a plastic material mounted on and engaging the threaded shaft, said contact carrier engaging at least one wall of the housing so as to prevent rotation of the contact carrier with the shaft by permitting the contact carrier to move longitudinally along the shaft as the shaft rotates; and

a metal contact carried by the contact carrier, said contact having one arm slidably engaging the resistance element and a second arm slidably engaging the collector member.

7. A potentiometer in accordance with claim 6 in which a metal terminal strip is secured to the collector member and extends through and projects beyond the bottom Wall of the housing, a boss projects from the housing around said collector member terminal strip, said collector member terminal strip having a notch in an edge thereof within its boss, and the boss extends into the notch to prevent movement of the terminal strip.

References Cited UNITED STATES PATENTS 8/1962 Berni 338-183 1/1967 Layland 388- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent'No. 3,412,362 November 19, 1968 John G. Woods et al It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

' In the heading to the printed specification, lines 4 and 5, "IRC, Inc.,Philadelphia, Pa." should read TRW Inc. a corporation of Ohio Signed and sea1ed-this3rd day'of March 1970.

(SEAL) Attest:

WILLIAM E. SCHUYLER, IR.

Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

